Fireplace Mantel Installation

Mantel Overview

When dealing with a new wood mantel, there are two major safety concerns: making sure the mantel isn’t too close to the fire, and securely attaching the heavy piece to the wall so it doesn’t fall over. Satisfying the first concern is a matter of ordering a mantel that is sized correctly for your fireplace. The National Fire Code says that all combustible material must be 1 inch away from the firebox opening for every 1/8 inch it protrudes from the surface, with a minimum 6-inch clearance all around. (If stricter local codes exist, these supersede national codes). If you have an odd-size firebox, a stock mantel may create a disproportionate-looking reveal around the opening, so you may have to custom order to get the mantel to look right. Satisfying the second concern is all about good carpentry. Many mantel-kit companies suggest merely toenailing the piece through the shelf directly to the wall, or even gluing it with silicone caulk. Since neither option is very sturdy, we recommend you attach the mantel to a cleat—a simple piece of lumber securely fastened to the wall. One cleat runs horizontally under the mantel shelf, and the others run vertically inside the legs (most mantels are hollow in back). Then you screw the mantel to the cleats along the back of the mantel shelf and the sides of the legs.

Fireplace Mantel Installation

1. Assemble the Mantel Pieces

Sand, then prime or stain the mantel before you begin. Wait until the mantel is installed to apply the final coat of paint or finish. Place the mantel shelf top-down on a tarp or rug. Slide the legs onto the shelf, slotting the dowels into their holes. Wiggle the legs as you apply slight pressure until the leg seams are tight. Twist the screws a quarter-turn to lock the cams. Hardware varies among manufacturers, but placing the shelf top-down and sliding the legs on is usually the safest method.

2. Dry-Fit the Mantel

Place the mantel against the wall (you may need a helper for this). Center it around the firebox. Place a 3-foot level across the mantel and check for level. Use a torpedo level to see if the shelf is level front to back. Tap shims under the legs as necessary until it’s level both ways. Lightly trace the mantel’s outline on the wall in pencil, as shown. This will give you a reference to help position the cleats.

Tip: Mantels are top-heavy. Allowing the shelf to tilt slightly back toward the wall helps hold it in place during installation. You’ll pull the legs flush with the wall as you screw to the cleat.

3. Position the Cleats

With the mantel face-down on the floor, measure the inside width of the shelf to determine the length of the horizontal cleat. Cut a 2x4 to this measurement and dry-fit it in place inside the shelf. (On some mantels, the cleats may have to be installed in pieces to accommodate blocking.) With the top cleat positioned, measure for the length and the depth of the vertical leg cleats. Cut 2x4 cleats (double up for a thicker mantel) and dry-fit them inside the legs.

Tip: Don’t wrestle with the cleats’ lengths—their position should be precise, but they don’t need to butt snugly together.

4. Bore the Pilot Holes

Measure the thickness of the mantel edges that will sit flush against the wall on the legs and shelf. Mark the distance on the wall at several points inside the pencil scribe of the mantel’s outline. Use the 3-foot level to connect the dots and mark where to hang the cleats. Hold the top cleat against the wall. Using a carbide-tipped masonry bit in a hammer drill, bore four evenly spaced ½-inch-diameter pilot holes through the cleats and into the brick.

Tip: Drill and screw into the brick, not the mortar. Brick is denser and will hold screws securely.

5. Attach the Cleats

If using a hammer drill, be sure to switch from hammer-drill mode to drill-only mode for this step. Fasten the cleat to the brick with 2 ½-inch concrete screws. Attach the side cleats in the same manner. Drive the screws through the pilot holes you previously drilled in Step 4.

Note: If you’re attaching the mantel to a conventional wood-stud wall, use 3-inch decking screws instead of concrete screws.

6. Install the Mantel

Fit the mantel over the cleats, aligning it with the outline marks on the wall. Press all edges flush against the wall before fastening. If the cleats are properly positioned, the mantel should fit over them like a sleeve. Turn off the drill’s hammer action. Use a driver bit to drive 2-inch finish screws every 16 inches along the back of the shelf above the center of the top cleat. Do the same through the outer edges of the legs (not the face) into the side cleats. Set the screwheads just below the surface so they can be concealed later.

7. Secure the Mantel

Use a Phillips screwdriver bit to drive 2-inch finish screws (a.k.a. trim head screws) every 16 inches along the back of the shelf above the center of the top cleat. Do the same through the outer edges of the legs (not the face) into the side cleats. Set the screwheads just below the surface so they can be concealed later.

8. Finish the Mantel

Using a hammer and 4d finish nails, attach thin pieces of edge molding along the mantel’s inner opening to cover the gap between the mantel legs and the brick. If you plan to paint the mantel, caulk any gaps along the wall. Putty over the screwheads (or fill them with plugs if you’re not painting). Apply the final coat of paint or finish.